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Date: Mon, 30 Aug 2021 10:27:38 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Lai Jiangshan <jiangshanlai@...il.com>
Cc: Tejun Heo <tj@...nel.org>, Marco Elver <elver@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Dmitry Vyukov <dvyukov@...gle.com>, walter-zh.wu@...iatek.com,
LKML <linux-kernel@...r.kernel.org>,
Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH] workqueue: Don't record workqueue stack holding
raw_spin_lock
On 8/29/21 8:18 PM, Lai Jiangshan wrote:
> On Sat, Aug 28, 2021 at 7:49 AM Shuah Khan <skhan@...uxfoundation.org> wrote:
>>
>> When CONFIG_PROVE_RAW_LOCK_NESTING and CONFIG_KASAN are enabled,
>> kasan_record_aux_stack() runs into "BUG: Invalid wait context" when
>> it tries to allocate memory attempting to acquire spinlock in page
>> allocation code while holding workqueue pool raw_spinlock.
>>
>> There are several instances of this problem when block layer tries
>> to __queue_work(). Call trace from one of these instances is below:
>>
>> kblockd_mod_delayed_work_on()
>> mod_delayed_work_on()
>> __queue_delayed_work()
>> __queue_work() (rcu_read_lock, raw_spin_lock pool->lock held)
>> insert_work()
>> kasan_record_aux_stack()
>> kasan_save_stack()
>> stack_depot_save()
>> alloc_pages()
>> __alloc_pages()
>> get_page_from_freelist()
>> rm_queue()
>> rm_queue_pcplist()
>> local_lock_irqsave(&pagesets.lock, flags);
>> [ BUG: Invalid wait context triggered ]
>>
>> Fix it by calling kasan_record_aux_stack() without holding pool lock.
>> There is no need to hold pool lock in this path.
>>
>> =============================
>> [ BUG: Invalid wait context ]
>> 5.14.0-rc7+ #8 Not tainted
>> -----------------------------
>> snap/532 is trying to lock:
>> ffff888374f32ba0 (lock#2){..-.}-{3:3}, at: get_page_from_freelist (mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165)
>> other info that might help us debug this:
>> context-{5:5}
>> 3 locks held by snap/532:
>> #0: ffff888139fa4408 (&type->i_mutex_dir_key#10){.+.+}-{4:4}, at: walk_component (fs/namei.c:1663 fs/namei.c:1959)
>> #1: ffffffffab870c40 (rcu_read_lock){....}-{1:3}, at: __queue_work (./arch/x86/include/asm/preempt.h:80 ./include/linux/rcupdate.h:68 ./include/linux/rcupdate.h:685 kernel/workqueue.c:1421)
>> #2: ffff888374f36cd8 (&pool->lock){-.-.}-{2:2}, at: __queue_work (kernel/workqueue.c:1466)
>> stack backtrace:
>> CPU: 14 PID: 532 Comm: snap Not tainted 5.14.0-rc7+ #8
>> Hardware name: LENOVO 90Q30008US/3728, BIOS O4ZKT1CA 09/16/2020
>> Call Trace:
>> dump_stack_lvl (lib/dump_stack.c:106 (discriminator 4))
>> dump_stack (lib/dump_stack.c:113)
>> __lock_acquire.cold (kernel/locking/lockdep.c:4666 kernel/locking/lockdep.c:4727 kernel/locking/lockdep.c:4965)
>> ? lockdep_hardirqs_on_prepare (kernel/locking/lockdep.c:4873)
>> ? lock_is_held_type (kernel/locking/lockdep.c:5368 kernel/locking/lockdep.c:5668)
>> lock_acquire (kernel/locking/lockdep.c:438 kernel/locking/lockdep.c:5627 kernel/locking/lockdep.c:5590)
>> ? get_page_from_freelist (mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165)
>> ? lock_release (kernel/locking/lockdep.c:5593)
>> ? __kasan_check_read (mm/kasan/shadow.c:32)
>> ? __lock_acquire (kernel/locking/lockdep.c:5019)
>> ? __zone_watermark_ok (./include/linux/list.h:282 ./include/linux/mmzone.h:111 mm/page_alloc.c:3908)
>> get_page_from_freelist (./include/linux/local_lock_internal.h:43 mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165)
>> ? get_page_from_freelist (mm/page_alloc.c:3665 mm/page_alloc.c:3703 mm/page_alloc.c:4165)
>> ? lock_is_held_type (kernel/locking/lockdep.c:5368 kernel/locking/lockdep.c:5668)
>> ? is_bpf_text_address (./arch/x86/include/asm/preempt.h:85 ./include/linux/rcupdate.h:73 ./include/linux/rcupdate.h:719 kernel/bpf/core.c:708)
>> ? lock_downgrade (kernel/locking/lockdep.c:5633)
>> ? __zone_watermark_ok (mm/page_alloc.c:4054)
>> __alloc_pages (mm/page_alloc.c:5391)
>> ? __alloc_pages_slowpath.constprop.0 (mm/page_alloc.c:5354)
>> ? create_prof_cpu_mask (kernel/stacktrace.c:82)
>> ? _find_first_bit (lib/find_bit.c:83)
>> alloc_pages (mm/mempolicy.c:2249)
>> stack_depot_save (lib/stackdepot.c:304)
>> ? lock_is_held_type (kernel/locking/lockdep.c:5368 kernel/locking/lockdep.c:5668)
>> kasan_save_stack (mm/kasan/common.c:41)
>> ? kasan_save_stack (mm/kasan/common.c:39)
>> ? kasan_record_aux_stack (mm/kasan/generic.c:348)
>> ? insert_work (./include/linux/instrumented.h:71 ./include/asm-generic/bitops/instrumented-non-atomic.h:134 kernel/workqueue.c:616 kernel/workqueue.c:623 kernel/workqueue.c:1335)
>> ? __queue_work (kernel/workqueue.c:1501)
>> ? __queue_delayed_work (kernel/workqueue.c:1657)
>> ? mod_delayed_work_on (kernel/workqueue.c:1720)
>> ? kblockd_mod_delayed_work_on (block/blk-core.c:1633)
>> ? __blk_mq_delay_run_hw_queue (block/blk-mq.c:1567)
>> ? blk_mq_run_hw_queue (block/blk-mq.c:1610)
>> ? blk_mq_sched_insert_request (block/blk-mq-sched.c:480)
>> ? blk_mq_submit_bio (block/blk-mq.c:2276)
>>
>> Fixes: e89a85d63fb2 ("workqueue: kasan: record workqueue stack")
>> Signed-off-by: Shuah Khan <skhan@...uxfoundation.org>
>> ---
>> kernel/workqueue.c | 18 +++++++++++++++---
>> 1 file changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>> index f148eacda55a..e647b29b9fb0 100644
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -1328,9 +1328,6 @@ static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
>> {
>> struct worker_pool *pool = pwq->pool;
>>
>> - /* record the work call stack in order to print it in KASAN reports */
>> - kasan_record_aux_stack(work);
>> -
>> /* we own @work, set data and link */
>> set_work_pwq(work, pwq, extra_flags);
>> list_add_tail(&work->entry, head);
>> @@ -1499,6 +1496,14 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
>>
>> out:
>> raw_spin_unlock(&pwq->pool->lock);
>> +
>> + /*
>> + * record the work call stack in order to print it in KASAN reports
>> + * Do this without pool raw_spinlock hold to avoid nesting raw
>> + * spinlock with page allocation spinlock.
>> + */
>> + kasan_record_aux_stack(work);
>> +
>
> Hello
>
> After the pool lock is released, the work item can be executed and be freed
> before kasan_record_aux_stack() is called. Is it Ok?
>
Right. That is a concern. As Dmitry pointed out there is a bug in the
code that kasan_record_aux_stack() is in the "out:" path.
> And I think queue_work() is allowed to be called with other raw_spin held.
> If it is the case, kasan_record_aux_stack() is still in raw_spin held section.
>
I looked for queue_work() -> queue_work_on() -> __queue_work() and
function header doc. I couldn't find any place it says it is okay to
call queue_work() with raw spinlock held.
I am thinking that is not the case, since __queue_work() acquires pool
lock which is a raw spinlock. The lockdep warning will occur when the
pool lock acquire happens. I haven't seen it. We have 1290 callers of
queue_work() and we would have seen this before.
thanks,
-- Shuah
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